This invention is in the field of cutting tools and processes for making a hole, threaded hole, or both in or on a work piece. More particularly, this invention relates to combined hole making and threading tools for a hand-held drill that require about no external axial force for advancement through a work piece after an initial pilot hole is created.
Related art has employed various tool structures for cutting holes, threads, or both in a work piece. Generally, tool structures are influenced by application and performance specifications. In the wake of the Space Shuttle Columbia tragedy, it was recognized that a need existed to perform field repairs of a spacecraft's Thermal Protection System (TPS), wherein the TPS is comprised of heat shield materials necessary for atmospheric re-entry. Field repairs in this unique application are comprised of repairing sections of broken leading edge materials and broken tile materials in the exoatmospheric space environment of Low Earth Orbit. The repairs must be made while the operator or astronaut is in a spacesuit. In this scenario of unique environment and unique wear, there are limitations to the applied axial and torsional forces allowed while in a spacesuit, due to the combination of a micro-gravity environment, the reaction forces between the space vehicle (e.g., Space Shuttle), and the platform supporting the suited astronaut. The apparatus and its multiple embodiments described herein serve to solve the unique problems that exist in the scenario described above.
Although the genesis of the apparatus, its multiple embodiments, and its methods of use originate in the scenario described above, there are many terrestrial applications where it is desirable to minimize the required axial force used to cut a hole, thread, or both in a work piece. However, available drill bit art requires significant axial forces to produce a hole. Further, required axial force loading for the related drill bit art is markedly increased as the hole-size becomes larger. It is not uncommon to require an axial force in excess of about 75 pounds to make holes from one-half to one inch in diameter. For large holes, drilling machines are the preferred apparatus since the required forces from a hand-held drill can become unobtainable, fatiguing, or both relative to an operator. In cases involving the operation of a hand-held drill, an operator generally exerts his/her body weight behind the drill to facilitate the cutting of a hole. Drilling “overhead” holes can be particularly exhausting for an operator. Repetitive drilling is fatiguing and limits operator productivity. Safety is also another important factor for hand-held drilling, especially for thinner work pieces. As the external axial force is increased, the likelihood of a drill bit grabbing the work piece and spinning the work piece, pulling the drill out of the operator's hand, or both becomes a threat to the operator's personal safety.
In related art, threaded holes and bores are most frequently produced with multiple tools, typically including a center or spot drill for centering the subsequent tools and creating an initial chamfer, a drill for creating the core hole or bore, a counterbore tool, and a tap for threading the hole. Further, there exist drill bits that make a single-sized hole, step drill bits that allow holes to be enlarged in a series of steps, taps that thread one size of a pre-existing hole, and drill-taps that first drill a hole with a drill bit fashioned after one for a single-sized hole and then tap after the hole is drilled.
In other related art, special drills are known which consolidate the center or spot drill, the drill for creating the core hole or bore, and the counterbore tool. This consolidation is accomplished by incorporating multiple diameters into the grind of the tool. However, the shape of such a tool is complex, and it is general expensive to manufacture and regrind. Since the diameters of the counterbore and chamfer are ground into the tool, they cannot be varied in use. Likewise, the length of the hole created in the work piece, as well as the relative lengths of portions of the bore, is dependent on the length of the corresponding portions of the tool which are predetermined.
U.S. Pat. No. 5,678,962 to Hyatt et al. discloses a unitary bore forming and threading tool for producing a variety of threaded boars having chamfers and counterbores without a need for tool change. The disclosed invention enables the creation of a variety of bores such as chamfers, counterbores, and threaded bores by producing bore portions of selectively determined distinct diameters by sequentially axially feeding the tool into a work piece along distinct tool paths without changing tools. This invention relies on moving the tool in a selective multi-axis path to form threads using a high-speed drilling machine or thread mill. Thus, this invention does not concurrently form a hole and cut a series of threads. Rather, this tool relies on separate and distinct hole-forming and thread-forming phases.
U.S. Pat. No. 6,012,882 to Turchan discloses a combined hole making, threading, and chamfering tool with staggered thread cutting teeth designed for a high-speed thread mill. Depending on the application, this invention can be fed into a work piece either linearly (along a predetermined longitudinal axis) or by multi-axis interpolation, including helical interpolation. However, threads are formed by helical motion and not along a predetermined longitudinal axis. Thus, this invention also relies on separate phases for hole creation and thread forming.
Thus, a need exists for an improved tool structure that cuts a hole, a thread, or both in a work piece with about no external axial force requirement for the tool's advancement through the work piece.